High body weight (obesity) is associated with what syndrome?
Metabolic syndrome -Abdominal obesity -High serum triglycerides -Low HDL cholesterol -High blood pressure -Risk of heart attack -Risk of stroke -Type II Diabetes Some Cancers (eg. breast and prostate cancers)
What is low body weight (malnutrition/undernutrition) associated with?
- Depressed immune function (risk of inception and infectious disease)
- Child mortality (biggest contributor worldwide - developing countries vs. developed countries)
- Muscle wasting
What is metabolism?
The sum of all the chemical reactions of the body, and is the conversion of chemical energy to other forms of energy.
What is the molecule that acts as the 'energy currency' of the cell?
an essential link between energy-utilizing and energy-producing functions of the body
Can be gained and spent repeatedly
What is the energy derived from the oxidation of carbohydrates, proteins, and fats used for?
To convert adenosine diphosphate into ATP which is consumed by various reactions
- active transport of molecules across cell membranes
- contraction of muscles and performance of mechanical work
- various synthetic reactions that create hormones, cell membranes, and many other essential molecules of the body
- conduction of nerve impulses
- cell division and growth
- many other physiologic functions
What is catabolism?
The set of metabolic processes that break down large molecules (include breaking down and oxidation).
Provide energy and components needed by anabolic reactions
What is anabolism?
The set of constructive metabolic processes where the energy released by catabolism is used to synthesize complex molecules such as proteins, polysaccharides, lipids and nucleic acids.
Anabolic reactions use ATP.
How is most ATP generated?
What is aerobic respiration?
- Requires oxygen and the breakdown of molecules such as glucose and fatty acids
- produce water and carbon dioxide.
- 50% of the energy released is used to synthesise ATP. The other 50% is lost as heat.
- ATP is hydrolysed to provide energy. 50% of this energy is used for anabolic reactions, mechanical work and the maintenance of electrochemical gradients across cell membranes. The other 50% is lost as heat. Therefore the overall efficiency of metabolism is 25%.
How is energy used in the body?
• mechanical work (skeletal muscle activity, pumping of the blood by the heart, movement of motile/ciliated cells)
• transport mechanisms (active ion and substrate transporters in cell membranes).
• chemical synthesis (synthesis of proteins, triglycerides, glycogen)
• signalling (hormone synthesis and release from endocrine glands)
• detoxification (urea formation, conjugation, oxidation and reduction reactions in the liver)
• heat production
What is 1 calorie?
The heat required to raise the temperature of 1g of water by 1oC
What is 1 kilocalorie?
heat required to raise temp of 1 kg of water by 1oC
SAME as 1 Cal (nb. different fom 1 cal)
What is 1 joule?
the energy exerted by a force of one newton acting to move an object through a distance of one metre.
What is 1 Newton?
the amount of force required to accelerate a mass of one kilogram at a rate of one metre per second per second
1 cal equates to how many joules?
What are the estimated 'average' daily requirement in kcal?
2000 kcal for a 55-year-old female
2500 kcal for a 55-year-old male
(3000 kcal for a young adult male with a moderate workload)
What is the metabolic rate?
The total rate of energy consumption by an individual
How can metabolic rate be estimated?
Direct Calorimetry: measure an individual's heat production - tricky to do
Indirect Calorimetry: measure an individual's rate of O2 consumption
- Carbohydrate metabolism releases 21 kJ (5 kcal) of energy for every litre of O2 consumed
- However the amount of oxygen consumed per kcal released depends upon the composition of the diet - Mixed diet: ~20.2 kJ (4.8 kcal) per litre O2.
Fat metabolism releases 4.7 kcal (19.7 kJ) per litre of O2 consumed
Protein metabolism releases 4.5 kcal (18.8 kJ) per litre of O2 consumed
What is the Basal Metabolic Rate?
The rate of energy expenditure by humans and other animals at rest, and is measured in kJ or kcal per hour.
50-70% of total energy expenditure
Differences in body size can be controlled for by dividing by body surface area (square metres). Rest is defined as existing in a neutrally temperate environment while in the post-absorptive state.
(The release, and using, of energy in this state is sufficient only for the functioning of the vital organs: the heart, lungs, nervous system, kidneys, liver, intestine, sex organs, muscles, brain and skin).
How can the Basal Metabolic Rate be measured?
Metabolism under a prescribed set of conditions which minimize the metabolic rate
Subjects should be well slept and at complete mental and physical rest
Subjects should be fasted for 12 hours.
Room temperature should be comfortable (thermoneutral).
Control (normalise) for differences in body size:
kJ (kcal) hr-1 m-2 of body surface area
(Ht 6 ft., wt 13 st., body surface area »2 square metres)
What happens to BMR with age?
BMR generally decreases with age and with the decrease in lean body mass (as may happen with aging).
Rate of change in amount of energy stored can be described as?
Rate of change in amount of energy stored =
rate of energy intake – rate of energy expenditure
Rate of change in amount of energy stored
is proportional to what?
Rate of change in body weight
How is energy stored?
In the form of glycogen and adipose tissue (fat).
What contributes to body weight?
How many kcal corresponds to approximately 1kg body weight?
Body weight is constant when...
Body weight is gained when...
Body weight is lost when...
energy intake rate equals energy expenditure rate (neutral energy balance).
energy intake exceeds energy expenditure (positive energy balance).
energy expenditure exceeds energy intake (negative energy balance).
In what situations is it desirable to have a positive engery balance (gaining weight)?
Growth in childhood
Recovery from illness or trauma
What types of situations increase energy expenditure?
- Exercise (demand of muscle contraction)
- Burns, trauma (hypermetabolic response)
- chronic illnesses such as such as heart failure, cancer, sepsis, rheumatoid arthritis, AIDs, cachexia, hyperthyroidism.
Body weight is well controlled considering the amount of food consumed in a lifetime
•9 tons carbohydrate
•3 tons protein
•3 tons fat
What increases appetite?
Where is it produced?
When is it produced?
Where it act?
The "hunger hormone", is a peptide produced by ghrelin cells in the gastrointestinal tract, mainly in the stomach and duodenum.
When the stomach is empty, ghrelin is secreted. When the stomach is stretched, secretion stops.
Ghrelin acts on hypothalamic brain cells to increase hunger. The receptor for ghrelin is found on the same cells in the brain as the receptor for leptin, the satiety hormone that has opposite effects from ghrelin.
What act to diminish appetite?
What is leptin?
Where is it made?
What does it regulate?
How does it do this?
The "satiety hormone"
A hormone made by fat cells
Regulates the amount of fat stored in the body.
It does this by adjusting both the sensation of hunger, and adjusting energy expenditures.
Hunger is inhibited (satiety) when the amount of fat stored reaches a certain level. Leptin is then secreted and circulates through the body, eventually activating leptin receptors in the arcuate nucleus of the hypothalamus. Energy expenditure is increased both by the signal to the brain, and directly via leptin receptors on peripheral targets such as skeletal muscle, liver, pancreas and adipose tissue.
What is Peptide YY?
A short (36-amino acid) peptide released by cells in the ileum and colon in response to feeding.
PYY acts to reduce appetite.
How does insulin affect appetite?
Insulin release from pancreatic islets cells follows intake of both carbohydrates and proteins.
Insulin dampens appetite by acting on the hypothalamus
How is BMI (body mass index) calculated?
Weight (in kilograms) divided by height (in metres) squared.
(BMI) = kg/m2
Is BMI a good indictation of obesity?
Not always when applied to individuals because of different body types.
However, BMI is still useful when assessing populations because these differences get averaged out.
Subjects may have a similar BMI and overall adiposity, but different adipose tissue distributions.
Differences in adipose tissue distribution convey a very different risk of metabolic disease.
- Thin outside fat inside
- Metabolically Healthy Obese
What is the lower limit for a healthy BMI?
What is the lower limit for an overweight BMI?
What is the lower limit for an obese BMI?
According to WHO - A BMI of under 20 kg/m2 indicates malnourishment (undernourishment); BMI between 25 and 30 kg/m2 indicates overweight; BMI over 30 kg/m2 indicates obesity.
What is the obesity epidemic?
The average BMI of the population in developed countries has been increasing steadily over the last several decades.
Widely considered to be a severe public health crisis.
Experts agree that as more and more obese children become obese adults, the diseases associated with obesity, such as heart disease, cancer, and especially diabetes will surge.
Why is the obesity epidemic occurring?
- YOUR FAULT = People can make a conscious choice to eat more and exercise less in a modern society. Those who do so don’t care about being obese, so any consequences are their fault.
- SOCIETY'S FAULT = Modern societies are increasingly ‘obesogenic’ in that there is more and more high calorie food available, and less and less need for physical activity. This has been imposed on the population, so the obesity epidemic is society’s fault.
- PARENT'S FAULT = Some people are genetically predisposed to obesity, in which case it is in a sense their parents’ fault.
What indicates that obesity isn't simply a conscious lifestyle choice i.e. willingly eating more and exercising less and accepting the consequences. ?
The existence of a multi-million dollar weight loss industry
What do these graphs indicate?
Possible changes over time in the population distribution of body mass index (BMI). An increasingly obesogenic environment would be expected to shift the whole population to a higher mean BMI (from the solid line to the dashed line in A) if there was no difference within the population in the tendency to gain weight in an obesogenic environment.
Several longitudinal studies have shown that the BMI distribution is skewed towards higher BMI and is becoming increasingly skewed in that direction (dashed line in B), indicating that some people are more susceptible than others to gaining weight in an increasingly obesogenic environment.
What is leptin deficiency caused by?
A mutation in the leptin gene.
Leptin suppresses appetite and promotes energy expenditure.
So people with leptin deficiency eat constantly and become morbidly obese.
This is an extreme example of the influence of genetics on BMI. However, this condition is very rare, with <30 cases known, so it can’t account for the obesity epidemic.
What is the FTO allele?
Fat mass and obesity associated gene (FTO)
At-risk allele associated with increased food intake
An allele that is associated with an increased risk of overweight and obesity.
Its effect is relatively mild but the prevalence is high, so it could explain why some people are more susceptible to an obesogenic environment than others
The product of the FTO gene is a mRNA demethylase. The risk allele is a cluster of 10 single nucleotide polymorphism in the first intron of FTO
(40% of Europeans carry one copy; weigh on average 1.2 kg more than people with no copies.
16% of Europeans carry two copies; weigh 3 kg more and have a 1.67-fold higher rate of obesity than those with no copies.
Carriers consume between 500 and 1250 kJ (125 and 280 kcal) per day more than non-carriers)
The genetic component explains what percentage of the variation in adiposity?
How can the obesity epidemic be explained?
Seems to be the interaction of the increasingly obesogenic environment with the genetic susceptibility of some people to weight gain in such an environment.
Disturbances in energy balance, body weight and adipose distribution carry...?